A while ago I posted that a trickle load had discharged my house batteries - 4 newish 6v wet batteries, 235 AH - and the cold snap froze them solid. Well, after crying for a few minutes I brought them into the heated shop and left them to thaw. Interestingly, frozen they had around .75v but when they thawed they came out to between 3.6 volts and 5.4 volts. They had crystals of something floating on top of the electrolyte. I added a little distilled water to bring the level to around 1/2" over the plates. My computerized chargers would not start on them, which I've seen before with highly discharged batteries, so I got out the "brute force" transformer based chargers, set them to 6v and got each battery up to around a charging level of 6 volts. At that point I connected them in two pairs in series and put my 10 amp three stage chargers on. I monitored them closely for about an hour, and the first thing I looked for was equal charging between the pairs. Both pairs had the batteries accepting equal charging voltages, around 6.2 volts at that early stage. I left them for around 24 hours, and both smart chargers took them through their cycle and switch to a float charge. I reset the chargers, and let them cycle again, this time noting that the voltages were still equal between all the batteries, and the peak voltage on the charge cycle got up to around 14.9 volts, which is exactly typical for both these chargers. All cells were off-gassing about equally and the crystals had disappeared. I took them off charge around 48 hours ago, and just checked - they are all at between 6.35 and 6.5 volts resting charge, which is telling me that at this point I might not have any dead cells, and they seem to actually have taken a real charge, not just a surface charge. I don't have a handy way to load test them. I think I may have dodged a bullet!

Same thing that happened to me with an airplane batt years ago! Glad yours worked out too.

One comment, most low amp smart chargers require that a batt have a min voltage before starting them. Also, they say not to attach the charger until the batt sits at least 8 hrs without either being charged or discharged. Yours may not say this but all mine do.

What I don't know is if smart chargers show the actual condition of a batt or just the voltage?

You can get a good load tester for around $20-30 at most any parts store or mail order like JCW or Harbor Freight. They are necessary, VMs only tell a small part of the story. I thing they come in 6v models but not sure of that.